1. Field of the Invention
This invention relates to a sensitized silver halide photographic material. More particularly, this invention relates to a silver halide photographic material containing sensitized fine silver halide crystals.
2. Description of the Prior Art
A photographic material containing fine silver halide particles, for example, those having an average diameter of 0.1 micron, is useful for recording minute images since images having a very small granularity and a superior sharpness can be obtained. However, the sensitivity of such a photographic material is generally lower than that of a photographic material containing relatively larger silver halide particles, for example, those having an average diameter of 0.6 micron, because the sensitivity of a silver halide photographic material generally tends to increase with larger sizes of silver halide particles. In general, therefore, the use of a photographic material containing fine silver halide particles requires large quantities of exposue and thus, a light source of a large luminous intensity or long exposure time, and this has set great limitation on the use of photographic materials containing fine silver halide particles. It is of great importance to increase the sensitivity of photographic materials containing fine silver halide particles to a level which is feasible for practical purposes.
Many methods have previously been known for increasing the sensitivity of a silver halide photographic material without increasing the particle size of the silver halide.
Among these are a method in which a sulfur compound such as sodium thiosulfate, a noble metal compound such as gold chloride, or other reducing agent such as tin chloride is added during the process of chemical ripening of a silver halide photographic emulsion, and a method in which immediately prior to coating, a quaternary ammonium salt-type compound, such as an alkyl pyridinium chloride or a polyoxyalkylene compound is added to a photographic emulsion.
These known sensitizing methods, however, cannot effect a sufficient elevation of the sensitivity without adversely affecting the photographic material containing the fine silver halide particles. Even when great sensitizing effects are obtained using these methods, a decrease in radient or fog may occur during storage of the photographic material.
A primary object of this invention is to provide a silver halide photographic material containing very fine silver halide particles in the photographic layer and having a high sensitivity.
A further object of this invention is to provide a photographic material containing fine silver halide particles which has a high sensitivity and a high gradient.
Another object of this invention is to provide a photographic material containing fine silver halide particles which has a high sensitivity and is free from fog during storage.